CurtPalme.com Home Theater Forum

[macgyver655]

Have you checked the heater voltage on this? I have not read everything.

[tschaeikaei]

This is the 8500 Ultra build in 2001. They have fixed heater voltage and i checked it some months ago.
Perfectly at 6.3V.
But the idea about rechecking it is not too bad. But i don't think it could cause that problem.
Heater voltage is fed to all three tubes from one rail on the LVPS, if it would cause the problem, it should appear on all three tubes, right?
As i say often: Correct me if i am wrong, i'm here to learn.
Regards, Julian

[thewolfman]

[Nashou66]

Those voltages are the same for all VNB's and the spot kill circuit will kill G2 to all tunes at the same time not just the VNB sending the signal.

Nashou

[macgyver655]

Does the glow at the back of the green tube by the neck board look any brighter then the red or blue?

[tschaeikaei]

[tschaeikaei]

[macgyver655]

I'm asking these questions because you have a hot heater. What you are seeing at startup is the deflection coming up and at shutdown you see the deflection collapsing. The problem is not the deflection but that you have electrons flowing during these processes. If you have tested with the mini coax cable disconnected like you claim you did then it is not the signal causing electrons to be emitted. So what you have left is possible heater problem.

1) Heater voltage to high? And yes, this could show an anomaly on only 1 tube. The green could be more susceptible then the other 2.
2) Damaged heater running hotter then normal even with correct voltage.
3) A minor short between heater and cathode.
4) Cathode or G1 short causing some electrons to be emitted. Although you really would not have full cutoff during normal running which I do not know if you have or not.

You have a rare abnormal issue so you have to look at rare and unusual possibilities.

Have you ran it with the mini coax for green disconnected at the neckboard?

[macgyver655]

Another thing just came to mind. Is every gnd connection on that green tube properly connected?

[tschaeikaei]

Now i understand this. Following you, the deflection behavior is normal.
It should happen, but should not be visible. The heater runs too hot and needs more time to cool down
to a temperature where it doesn't emmit electrons then it should.

1. Will recheck this.
2. That should be detectable measuring the heater DC resistance, right?
3. That maybe could be detectable measuring the DC resistance between heater and cathode, right?
It could be possible even with infinite ohms between heater and cathode, measured with an ohmmeter, right?
4. I played with the G2 settings, but i know the initial setting for green, where i started.
It was 61 for G2.

I didn't run it without the mini coax connected, i ran it with the blue mini coax on the green VNB.

[tschaeikaei]

One more: It should make sense to measure the current flowing through the heater and to compare it to the other tubes heater current.

[tschaeikaei]

I killed an IC on the vertical board while taking measurements. Is the clicking noise on the vertical board normal?
The des IC is a TL084CN, called U901. I have some TL084ACN here, can i exchange it with one of those?

Regards, Julian

[macgyver655]

You should be able to use the ACN. The minor differences should be fine.

You are wasting your time doing any measurements other then rechecking the heater voltage, testing with the video cable disconnected and checking tube grounds. Your problem would be with the tube itself and only possible saving it would be with a Sencore 7000.

Are you saying you tried dropping your G2, 10 or 20 points and shut down and restarted and the issue was still there, with no change?

The anomaly at startup I would not worry about since it is scattered and dim. The shutdown one concerns me but it is hard to tell how bright it is. But on the other hand, if the problem is the tube and is not repairable, then running it doesn't matter if it gets damaged eventually or not. The problem may even go away over time. But you only have a few things left to check to verify, short of swapping out the tube.

[tschaeikaei]

I swapped the TL084ACN in but no, there must be an additional failure.
The red V-Fail LED at the CLM came on after some time running.
I just wanted to find out where that noise on the vertical board (audible noise, one could hear it)
comes from. And i slipped off with the test probe and connected pin11 and pin 12 of U901 with them.
A small spark at the probe and the tubes are dark.

Now, after swapping the ICs, the projector started. All diagnostig LEDs were off.
The relais clicked, but there was no HV on.
After about 1min, the V-Fail LED came on.
I have a schematic of the vertical board here, but no idea what to look after.
I'm not sure, if it was pin 11 and 12 i shorted. But on this side of the chip.
Could be that i shorted 12 to 13 or 10 to 11.

I measured the resistors /capacitors and diodes near by and compared the measurements
to the other v-board (working condition) i have here.
Same revision number.

Any idea, how to go further?

schematic

Thank you, Julian

[Tim in Phoenix]

Hello

A small buzzing noise from the vertical board is normal; the most you can do is hot-glue the capacitors to muffle the sound a little.

[tschaeikaei]

Ok, thanks Tim. So the sound comes from the capacitors? I didn't think those can produce a sound.
The only electronic part i know to produce noise is coils.. But nice to know this.
Do you have an idea about the V-Board?
I have exchanged it with the V board of the other 8500U i have here.
Now the projecotrs runs again. But i don't know where to start the repair.
Maybe you could look in the schematic and tell me where to measure.
I found out that pin 11 goes to the -14,5V Vcc.

Regards, Julian

[tschaeikaei]

Now running with the other vertical board.
Heater voltage is 6,25V at green and 6,27V at the blue tube, measured without the green video mini coax connected.
Measured heater resistance before, it was about 6.xx Ohm at green and at blue.
Don't remember the exact reading, but they were the same.
The heater at the green tube is as bright as the blue. (Looking through the neckboard).
I measured between heater pins (9 and 10) and the other pins.
Infinite Ohm from heater to every other pin.
To go on further to detect a "soft" short between heater and anything else, i would need a tube tester
or a insulation tester. Have neither of those.

[tschaeikaei]

HA! Fixed it. There is an 1Ohm fusible resistor (R06) on the -15V rail. It had infinite ohms.
Changed it and the same resistor R06 on the +15V rail too to get symetrical voltages again.
Vertical board working again.

Green tube problem stays where it was in the beginning.

Regards, Julian

[Tim in Phoenix]

Hello

Could be your ribbon cable was shifted off a pin sideways, I blew some resistors that way

[tschaeikaei]

Hey Tim, i know where the blown resistor came from.
I took some measurements at U901 and slipped with the probe.
So the probe shorted pin 11 and 12. Changed R05 and R06 and thats it.
Typo in my last post. R05&06...

Regards, Julian